Cracking of a gas oil with zeolite and nonzeolite catalyst

ABSTRACT

A GAS OIL IS PASSED THROUGH A SOLVENT EXTRACTION ZONE TO SEPARATE AN AROMATICS-RICH EXTRACT FRACTION FROM AN AROMATICS-LEAN RAFFINATE FRACTION. THE AROMATICS-RICH EXTRACT FRACTION IS DISTILLED TO SEPARATE A LIGHT GAS OIL EXTRACT FRACTION FROM A HEAVY GAS OIL EXTRACT FRACTION. THE AROMATICSLEAN RAFFINATE FRACTION AND THE LIGHT GAS OIL EXTRACT FRACTION ARE CRACKED IN A FLUID ZEOLITE REACTION ZONE WITHOUT ADDED HYDROGEN TO PRODUCE A FIRST GASOLINE PRODUCT. THE HEAVY GAS OIL EXTRACT FRACTION IS CRACKED IN A FLUID NONZEOLITE CRACKING ZONE WITHOUT ADDED HYDROGEN TO PRODUCE A SECOND GASOLINE PRODUCT. THE FIRST AND SECOND GASOLINE PRODUCTS ARE BLENDED.

R. W. KOCH Oct. 3, 1972 CRACKING OF A GAS OIL WITH ZEOLITE ANDNONZEOLITE CATALYST Filed July 23, 1970 www n www wwf/WOR. @oaf/er n4KOC/f United States Patent O 3,696,023 CRACKING OF A GAS OIL WITHZEOLITE AND NONZEOLITE CATALYST Robert W. Koch, Verona, Pa., assignor'to Gulf Research & Development Company, Pittsburgh, Pa. Filed July 23,1970, Ser. No. 57,507 Int. Cl. Cg 11/04 U.S. Cl. 208--87 l 4 ClaimsABSTRACT OF THE DISCLOSURE A gas oil is passed through la solventextraction zone to separate an aromatics-rich extract fraction from anaromatics-lean raffinate fraction. The aromatics-rich extract fractionis distilled to separate a light gas oil extract fraction from a hea-vygas oil extract fraction. The aromaticslean rainate fraction and thelight gas oil extract fraction are cracked in a fluid zeolite reactionzone without added hydrogen to produce a 'lirst gasoline product. Theheavy gas oil extract fraction is cracked in a iluid nonzeolite crackingzone without added hydrogen to produce a second gasoline product. Therst and second gasoline products are blended.

The present invention relates to cracking of a gas oil hydrocarbon whichprior to cracking is passed through an aromatics extraction zone toseparate an aromatics-rich extract fraction from an aromatics-leanrailinate fraction.

The present invention relates to cracking in a nonhydrogen atmosphere ofaromatics-rich and aromatics-lean fractions of a gas oil hydrocarbon inthe presence of a iluid noncrystalline, i.e., amorphous, silica aluminanonzeolite cracking catalyst and a lluid crystalline aluminosilicatezeolite cracking catalyst, respectively. According to the prior artmethods wherein cracking was carried out in the presence of hydrogenunder both hydrogenation and cracking conditions, it was found that highboiling polynuclear aromatics are hydrocracked more efliciently over anonzeolite catalyst than over a zeolite catalyst, while the lowerboiling monoaromatics are hydrocracked more eiiiciently over a zeolitecatalyst. Therefore, the prior art teaches that in hydrocracking a wideboiling range gas oil as much as possible of the higher boiling(polynuclear or fused ring) aromatics should be concentrated in a streamfed to a nonzeolite catalyst chamber while as much as possible of thelow boiling aromatics should be concentrated in a stream fed to azeolite catalyst chamber. According to the prior art teaching, it wouldappear that distillation of the Wide range gas oil feed into a light gasoil fraction and a heavy gas oil fraction would be an effective meansfor preparing the feed to the two zones. However, in accordance with thepresent invention we have found that more eicient cracking in a zeolitezone occurs when a low-aromatics feed having the same wide boiling rangeas the full range gas oil is charged to the zeolite chamber than if thesame feed is diluted with a light gas oil.

In accordance with the present invention which relates to cracking in anonhydrogen atmosphere, it has been found that after solvent extractionof a wide-boiling range gas oil hydrocarbon stream to produce anaromatics-rich extract stream for charging to a nonzeolite crackingchamber and an aromatics-lean raffinate stream for charging to a zeolitecracking chamber, with the extract and rainate` streams each havingabout the same Wide-boiling temperature range as the feed gas oil, thelow-boiling aromatics fraction in the extract stream does not exert itsexpected effect in the process based upon the experience of the priorart in hydrocracking. After conventional solvent extraction of a gas oilthe extract fraction is relatively rich in aromatics and because of itswide boiling range it includes Y both high-boiling polynuclear aromaticsand lower-boiling 3,6%,Z3 Patented Oct. 3, 1972 r'ice Y nucleararomatics and lower-boiling mononuclear aromatics. Based upon theteaching of the prior art with respect to hydrocracking it would beexpected that the advantage of the solvent extraction operation is toremove the highboiling polynuclear or fused ring aromatics from theraffinate feed to the zeolite cracking chamber, while the removal oflower boiling mononuclear aromatics, if unavoidable, is not desirable inthe hydrocracking operation and for best results, in the zeolitecracking chamber, particularly, the lower boiling aromatics which wereremoved and are in the extract phase which is destined for thenonzeolite chamber should be fractionated from the extract phase andadded to the raffinate feed to the zeolite cracking chamber.

`It is a surprising discovery in accordance with the present inventionin regard to cracking in a nonhydrogen atmosphere that, following thearomatics extraction step, the removal of the light gas oil fractionfrom the extract phase destined for the nonzeolite chamber and theaddition thereof to the rainate feed to the zeolite chamber has adeleterious effect in the zeolite cracking operation in regard to bothtotal conversion and gasoline yield, because this is contrary to theexperience of the prior art in regard to hydrocracking. Therefore, thedilution of the wide boiling range rafnate feed containing polynucleararomatics with light gas oil which is relatively more rich inmononuclear aromatics had an adverse effect upon cracking efficiency inthe zeolite cracking zone. As stated, this effect is unexpected in viewof the prior art experience in hydrocracking which indicates thatenrichment of the feed to the zeolite zone with mononuclear aromaticsand dilution of polynuclear aromatics is beneficial. This effect alsoshows an advantage in solvent extraction as a method for feedpreparation over simple fractionation of a full range gas oil into twonearly equal fractions; one fraction comprising mostly light gas oilfeed for the zeolite zone and the other fraction comprising mostly heavygas oil feed for the nonzeolite zone. The simple fractionation methodconcentrates nearly the entire light gas oil fraction in the feed forthe zeolite zone in contrast to the experience of the present inventionwhich shows an adverse effect in said zone upon increasing theconcentration of light gas oil therein.

The' above-described discovery is not only surprising in regard to theprior art Iteaching regarding Ihydrocracking but is also surprising inregard to experience in the prior art concerning lcracking of gas oil ina non-hydrogen atmosphere in the presence of a zeolite catalyst. It hasbeen the experience of the non-hydrogen zeolitic cracking art that thehigher boiling aromatics in general Were deleterious feed constituentswhile lower-boiling :aromatics were advantageous feed constituents forgasoline production. y'Ille reason is that higher boiling aromatics,such as bicylclics, do not crack easily and tend to be absorbed upon azeolite catalyst to lower yits activity. Unlike monocyclics, which crackeasily in the presence of a zeolite catalyst, the higher boilingaromatics tend .to polymerize to form coke. In contrast to the presentinvention, the prior art experience would tend to indicate that dilutionof a Wide boiling rainate feed to a zeolite cracking zone with light gasoil would enhance cracking eiciency in said zone.

It has been found that in a combination non-hydrogen cracking processutilizing both zeolite and nonzeolite catalyst the transfer of the lightgas oil from the extract phase to the rainate phase induces more than acompensating rise in activity in the nonzeolite chamber to overcome theloss of activity in the zeolite chamber. In the combination process, afull range gas oil is solvent extracted to produce a wide boiling rangearomatics-rich extract phase, which is more advantageously cracked inthe presence of a nonzeolite catalyst than a zeolite catalyst, and toproduce a wide boiling range aromatics-lean raffinate phase which ismore advantageously cracked in the presence of a zeolite catalyst than anonzeolite catalyst. When the light gas oil fraction is separated fromthe extract phase feed to the nonzeolite cracking chamber and blendedwith the raflinate phase feed to the zeolite cracking chamber, thegasoline yield in the zeolite cracking chamber is reduced. However, thegasoline yield in the nonzeolite chamber is increased by more than acompensating amount so that when the gasoline products from the zeoliteand nonzeolite cracking chambers are blended, a higher gasoline yield, ahigher octane number and a higher total conversion are achieved than ina similar combination process except that the light gas oil fraction isnot removed from the extract phase feed to the raflinate phase.

In all cracking zones of this invention, cracking occurs without addedhydrogen at a temperature of about 850 F. to l100 F., or more. Thepreferred range is 880 F. to 1000 F. The total pressure can vary widelyand can be, for example, to 50 p.s.i.g., or preferably 20 to 30 p.s.i.g.In the zeolite and nonzeolite fixed iiuid bed chambers of FIGS. 1through 4, space velocities of 2 to 12 W./H./W. can be employed.

The full range gas oil feed to the process of the invention can have anI.B.P. of 450 to 500 F. and an E.P. of 1000 to 1050 F. The materialreferred to herein as light gas oil, such as the material which isremoved from the extract phase and added to the ratlinate phase, canhave a boiling range of 450 to 650 F. Heavy gas oil therefore will havea boiling range from 650 to 1000 or 1050 F. The light gas oil fractioncan slightly overlap the heavy gas oil fraction in which case its E.P.will be about 670 F. The solvent used for aromatics extraction in thetests described below was furfural.

The cracking operation with both zeolite and nonzeolite catalyst occurswithout hydrogen addition to the reactor and therefore occurs withoutnickel or other catalytic hydrogenation metal on the catalyst. Since thecracking atmosphere does not contain hydrogen the aromatic rings are notsaturated and are difiicult to crack, which accounts for the basicdistinction between the present process and hydrocracking.

FIG. 1 shows a simple process for uid bed cracking with a nonzeolitecatalyst. A full range gas oil as described at A in the data of Example1 is charged through line 10 to fluid nonzeolite catalyst crackingchamber 12. An eluent stream as described at J in the data of Example 3is recovered through line 14 while a portion of the eluent is recycledthrough line 16.

FIG. 2 shows a simple process for fluid bed cracking with a zeolitecatalyst. A full range gas oil as described at A in the data of Example1 is charged through line 18 to fluid bed zeolite catalyst crackingchamber 20. An etiiuent stream as described at K in the data of Example3 is recovered through line 22 while a portion of the eiiiuent isrecycled through line 24.

In the process scheme of FIG. 3 a full range gas oil as described at Ain the data of Example 1 is charged through line 56 to extraction zone58 utilizing furfural as a solvent from which zone a low aromaticsraffinate is recovered as described at D in the data of Example 1through line 60 and a high aromatics extract as described at E in thedata of Example 1 through line 62. The raffinate in line 60 is chargedto reactor 64 containing a fluid bed of zeolite catalyst whichdischarges an effluent stream through line 66 as described at I in thedata of Example 2, a portion of which is recycled through line 68. Thehigh aromatics extract in line 62 is charged to fluid bed nonzeolitecatalyst reactor 70 from which an effluent stream as described at H inthe data of Example 2 is discharged through line 72, a portion of whichis recycled through line 74. The individual effluents in lines 66 and 72can be removed from the system through lines 67 and 73,

respectively, and can be individually utilized as sources of leaded orunleaded gasoline stocks, or the two entire effluent streams can bemerged in line 75 to provide a total process product as described at Min the data of Example 3.

In FIG. 4 a full range gas oil as described at A in the data of Example1 is charged to an aromatics extraction unit 28 utilizing furfural as asolvent from which unit a low aromatics raffinate fraction is removedthrough line 30 while a high aromatics extract is removed through line32 and passed to a distillation zone 34. Zone 34 discharges a light gasoil extract fraction through line 36 which blends with the low aromaticsraflinate in line 30 to pr0 duce the feed in line 38 as described at Bin the data of Example 1 which is charged to the iiuid zeolite catalystbed reactor 40 having recycle line 42 and effluent line 44 whosecomposition is shown at G in the data of Example 2. Distillation zone 34discharges a heavy gas oil extract eiuent through line 46 as describedat C in the data of Example 1 which is charged to nonzeolite fluidcatalyst bed reactor having a recycle line 50 and a discharge line 52containing an eiiiuent stream as described at F in the data of Example2. The effluents from lines 44 and 52 can be removed from the systemthrough lines 4S and 53, respectively, and can be used as individualsources of leaded or unleaded gasoline stocks or the two entire efiluentstreams can be merged in line 54 to produce a combined product asdescribed at L in the data of Example 3.

Following are the operating conditions employed for the FCC zeolite andnonzeolite reactors shown in FIGS. 1 through 4.

The fractionation of the feed by means of solvent extraction inaccordance with the present invention produces a much more effectivedistribution of aromatics between two phases than could be achieved bysimple fractionation into relatively high and low boiling fractions. Forexample, in accordance with the present invention, the extract commonlycontains at least twice the concentration of aromatics as the raffinate.More commonly, the extract contains 3, 4 or 5 times and more aromaticsthan the raiiinate. Any known aromatics solvent can be employed for theextraction. Solvents known in the art include methanol, ethanol, phenol,furfural, ethylene glycol, monomethyl ether, acetonitrile, sulfurdioxide, etc. The solvents resolve a full range gas oil into a higharomatics extract phase and a low aromatics ranate phase, each phasehaving substantially the full boiling range of the feed gas oil and eachphase tending to contain monoaromatics in its lower boiling portion andpolynuclear or fused ring aromatics in its higher boiling portion. Thistype of separation is contrasted with distillation of a full range gasoil fraction into two equal phases in which case the amount of aromaticsare about equal in the two phases with the monoaromatics tending to beconcentrated in the lower boiling fraction and the polynuclear or fusedring aromatics tending to be concentrated in the higher boilingfraction. The type of aromatics distribution achieved by distillation isnot equivalent to the type of aromatics distribution achieved by solventextraction in accordance with the discovery of this invention becauseunder the distillation method of aromatics distribution line, but withcomparable octane numbers, as compared the heavy gas oil phasecontaining most of the polyto stream I, described below, which relatesto treatment nuclear aromatics is charged to the nonzeolite catalyst ofa full range feed with nonzeolite catalyst only.

chamber leaving the light gas oil phase containing substantially most ofthe monoaromatics in the feed for the 5 EXAMPLE 3 zeolite catalystchamber, whereas it has now been dis- The following table describes thecombined FCC unit covered that dilution of a wide boiling rangeraffinate yields referred to in FIGS. 1 through 4 of the drawings.

COMBINED FCC YIELDS REFERRED TO IN FIGURES l THROUGH 4 Drawingdesignation J K L M Zeolite FCC run:

Percent oi iull range gas oil charge 100 72.4 63.9. Fraction chargedFull range gas oil.. Ranate and light extract.. Raftinate. NonzeoliteFCC run:

gement iulll range gas oil charge iEtll ..1 2137.6 36.1. raction c argerange gas i eav extract E combined Fco yields: y ma Conversion, volumepercent 69.5 79 2 80 5 Debutanized gasoline, volume percent 48.2.--.Cri-gasoline, volume percent 37.2 C5-C5=, volume percent 11.0...-C4-C4=, volume percent 15.3.--. C;-C;=, volume percent 10.1 C2 andlighter, weight percent.. 4.1 Coke, weight percent 9.1- Motor, clear79.7 Research, clear 93.6 91 5 feed to a zeolite cracking zone withlight gas oil performs An important feature indicated in the above datais a deleterious effect upon gasollne y1elds 1n the zeolite that streamM which is the result of treatment with both cracking zone. zeolite andnonzeolite catalyst exhibits a higher total The following examplespresent typical feed stock data conversion and a higher conversion todebutanized gasoand actual and mathematical model yields based upon linethan stream K which is the result of treatment of correlations from manyfeeds for the described processing the total feed with zeolite catalysteven though stream I schemes. shows that treatment of any portion of thefeed with a EXAMPLE1 30 nonzeolite catalyst would be expected to reduceboth The following table presents the properties of the FCC totalconversion and conversion to debutanized gasoline.

A further highly important feature of the above data feedstocks referredto m FIGS 1 through 4 of the is the showing that the unexpectedly hightotal conversion drawings.

v PROPERTIES OF THE FCC FEEDSTOCKS REFERRED TO IN FIGURES 1 THROUGH 4Drawing designation A B C D E Catalyst in unit where charged. Nonzeoliteor zeolite-. Zeolite Nonzeolite zeolite Nonzeolite, Name o! stock Fullrange gas oil Rafiinate and iight extract-- Heavy extract... Raiuate-F1111 range extract.

Grav1ty,API 23.9- 30.0 8.5 32.0 10.2.

ulfur, wt. percent 2.63. 1.53. 5.78 1.06 5.59. Nitrogen, wt. percent0.066 0.010 0.205 0.011 0.171. Annine point,F-. 170 102 79 207 75. ASTMl0%, F 589.- 571.- 752 583 605. ASTM 3o%, F 715 645 807 677 731. ASTM F799--.. 765 862 813 ASTM F 876 883 927 902 894 ASTM 9o%, F 958--.984---- 983 ese 970. Fraction light gas oil (B.P. below 650 F.) 0.1930.241 0 0.303 0,164 Mean avg. boiling point, F 761 757 855. 736 777.Fraction aromatics 0.238 0.139 0.588 0.170 0.562.

EXAMPLE 2 and conversion to debutanized gasoline as well as octanenumbers exhibited by stream M are further enhanced in stream L, which isthe blended product of lFIG. 4. In accordance with the presentinvention, with special ref- The following table describes theindividual yields of 50 the FCC Vunits referred to in FIGS. 1 through 4of the drawings.

INDIVIDUAL FCC YIELDS REFERRED TO IN FIGURES 1 THROUGH 4 Drawingdesignation F G H 1 Catalyst type Nonzeolite Zeolite Nonzeoiite zeolite,Fmi mak Heavy extract... Ratnate and light extra Full range extract...Ratlnate. FCC yields:

Conversion, volume percent 66.9

Dcbutanized gasoline, volume p cent 44.4 Orl-gasoline, volume percent.-.

(J5-CF, volume percent- 8.8

C4-C4=, volume percent.. 12.6

C;-C3=, volume percent 9.5

C; and lighter, weight percent- 5.5 4.4

Coke, weight percent 15.2

Moto ear 79.2-

Research, clear 94.4 91 8 94 4 The above data show that low aromaticsraffinate erence to FIG. 4, it has been found that the light gas oilstream I from the zeolite reactor exhibits a greater portion of theextract stream has a marked effect upon total conversion and a greaterconversion to debutanized gasoline yield in both the zeolite andnonzeolite chambers. gasoline, but with lower octane numbers, ascompared to 70 Referring to the data in Example 2, it is seen that whenstream K, described below, which vrelates to treatment of the full rangeextract is distilled to remove the light gas a full range feed withzeolite only. `O11 the other hand, oil (450 to 650 F.) fractiontherefrom to produce a the above data show that high aromatics extractstream heavy extract having no light gas oil, and the removed H from thenonzeolite reactor exhibits a lower total light gas oil is added to theraffinate to produce a raflinate conversion and a lower conversion todebutanized gasoplus light extract stream, the gasoline yield from theex- 7 tract was increased from 42.6 to 44.4 volume percent while thegasoline yield from the raffinate was decreased from 64.3 to 61.3 volumepercent. It is seen that removal of the light gas oil from the extractincreased gasoline yield from that stream and the addition of the lightgas oil to the rafinate stream decreased gasoline yield from thatstream. This effect is surprising since the prior art teaches in regardto hydrocracking that it is the transfer of only high boiling aromaticsto the rainate feed to a zeolite cracking reactor which is detrimentaland that lower molecular weight monoaromatics are advantageouslytransferred from a nonzeolite cracking zone feed to a zeolite crackingzone feed to improve eiciency in said zeolite zone.

EXAMPLE 4 The following data illustrate that the large difference inaromatics concentration in ranate and extract streams from solventextraction is not achieved through distillation of the feed. The lirsttwo columns of the following data show zeolite cracking feed stockshaving large differences in mean average boiling point but relativelyminor differences in aromatics content. The second two columns of thefollowing data show zeolite cracking feed stocks having smallerdifferences in mean average boiling point but greater diiferences inaromatics content. The data therefore indicate that distillation of acracking feed into fractions of widely different mean average boilingpoints will not necessarily produce wide differences in aromaticsconcentration.

8 upon a raflinate feed as described above to reactor 64 and the productcharacteristics based upon a full range extract feed as described aboveto reactor 70.

The following data show the characteristics of the combined feed fromthe two zeolite reactors.

Zeolite FCC runs:

Percent full range gas oll charged 63. 9 Fraction charged Ranat CombinedFCC yields:

Conversion, vol. percent Debutanized gasoline, vol. percentCri-gasoline, vol. percent C-CF, vol. percent Cl- C4=, vol. percentCg-CF, vol. percent C; and lighter, weight percent Coke, wt. percentMotor, clear Research, clear 36. 1 Extract Comparing the productcharacteristics presented above of the combined product stream from twozeolite reactors High light gas oil in feed Feed preparation Gravity,API. Sulfur, wt. percent.

The cracking data presented in the above table show that greatdifferences in feed aromatics concentration, regardless of averageboiling point of the feed, have a much greater effect upon totalconversion and gasoline yield in a zeolite reactor than do greatdifferences in average boiling point of the feed accompanied by smallervariations in laromatics content.

EXAMPLE 5 Data were taken to illustrate the criticality to the presentinvention of employing an amorphous nonzeolite catalyst chamber inconjunction with a zeolite catalyst chamber, rather than employing twoseparate zeolite catalyst chambers. The data relate to a process asshown in FIG. 3, except that chamber 70 contains a zeolite catalystrather than a nonzeolite catalyst and the operating conditions for azeolite chamber as presented above were adopted, while chamber 64continues to contain a zeolite catalyst. The feed stock and operatingconditions are otherwise unchanged from those used in the process ofFIG. 3. The following data Show the product characteristics based Lowlight as o1 ln feed g Low aromatics in feed High aromatics in feed withthe product characteristics of the combined product stream M from theprocess of FIG. 3, it is seen that use of both a zeolite and anonzeolite catalyst chamber rather than two zeolite catalyst chambersresults in a considerably higher gasoline yield, a higher octane numbergasoline product, and a lower coke yield.

I claim:

1. A process for cracking a feed gas oil comprising passing said gas oilto an aromatics extraction zone, separating an aromatics-rich extractfraction for cracking without saturating the aromatic rings from anaromatics-lean raflinate fraction in said zone, distilling saidaromaticsrich extract fraction to separate a light gas oil extractfraction from a heavy gas oil extract fraction, cracking said ratiinatefraction and said light gas oil extract fraction in the presence of afluid crystalline aluminosilicate zeolite cracking catalyst withoutadded hydrogen to produce a rst gasoline product, cracking said heavygas oil extract fraction in the presence of a fluid amorphous silicaalumina nonzeolite cracking catalyst substantially free of zeolitewithout added hydrogen to produce a second gasoline product and blendingsaid rst and second gasoline products.

2. The process of claim 1 wherein the concentration of aromatics in saidaromatics-rich extract fraction is at least 'about twice as high as theconcentration of aromatics in said aromatics-lean raffinate fraction.

3. The process of claim 1 wherein the concentration of aromatics in saidaromatics-rich extract fraction is at least about three times as high asthe concentration of aromatics in said aromatics-lean ratinate fraction.

4. The process of claim V1 wherein the boiling range of saidaromatics-lean rainate fraction is substantially as wide as the boilingrange of the feed gas oil.

References Cited UNITED STATES PATENTS 3,331,766 7/ 1967 Young 208-87 53,159,567 12/ 1964 Young 208-87 2,279,550 4/1942 Benedict et al 208-873,080,31-1 3/ 1963 Mertes 208-78 2,304,289 12/ 1942 Tongberg 208--873,210,267 10/ 1965 Plank et a1. 208-120 -HERBERT LEVINE, PrimaryExaminer Us. c1. X.R.

